Fluid ejection devices are provided with fluid ejection heads for ejecting fluid onto a substrate. Fluid ejection heads are provided with one or more nozzle arrays for ejecting the fluid. Some fluid ejection devices are provided with successive nozzle arrays or print bars that are arranged successively and parallel to a substrate advance direction. Drive systems advance the substrate with respect to the successive nozzle arrays during fluid ejection. The drive systems can exhibit tolerances or imperfections.